1. Field of the Invention
The invention relates to a vessel, and more particularly to a vessel which will initially permit the passage of microwave electromagnetic energy to heat the contents of the vessel until such time that the internal temperature of the vessel contents reaches a preselected level, at which time the vessel will shield the contents from the microwave energy.
2. Description of the Prior Art
The vessel of the present invention and the various embodiments thereof to be described have many uses. The material to be contained within the vessel does not constitute a limitation of the present invention and the vessel may be so constructed as to be used with electromagnetic energy of various wave lengths, as will be evident hereinafter.
For purposes of an exemplary showing, the vessel and its various embodiments will be described in their application as vessels for foods to be prepared in a microwave oven.
In recent years the use of microwave ovens to heat or cook foods has increased markedly both in the home and in commercial establishments. This is true for numerous reasons. For example, microwave ovens require no pre-warming, heat efficiently and result in energy savings. Many foods demonstrate a superior taste when prepared in a microwave oven and retain more of their nutritional components. They are perhaps best known for the speed with which they heat or cook and they offer both the homemaker and the commercial establishment rapid reheating of refrigerated pre-cooked foods.
Microwave ovens are not, however, without certain disadvantages. For example, heating or cooking by means of a microwave oven is so rapid that an error of several minutes can make the difference between a well done roast and a rare roast or properly cooked foods and over-cooked foods. Each food product, itself, possesses characteristics having a marked influence on cooking or heating time. For example, such factors as the quantity of the food product to be heated or cooked, the size of the food product, the shape of the food product, its consistency and its dielectric properties all influence the rapidity and uniformity with which it will be heated or cooked in a microwave oven. Furthermore, microwave ovens by different manufacturers differ in power outputs. Most domestic microwave ovens are produced with power outputs in the range of 600 watts to 1000 watts at a nominal frequency of 2,450 million cycles per second (2,450 MHZ). The nominal wavelength at this frequency is 12.2 cm (4.8 inches). Another nominal frequency assigned to microwave cooking is 915 MHz with a nominal wavelength of 33 cm (12.9 inches). Finally, the microwaves within the oven chamber tend in some places to reinforce each other and in other places to cancel each other with the result that a food product being heated or cooked in the microwave oven will often demonstrate hot and cold spots, adversely effecting the uniformity of heating or cooking.
All of the above noted factors result in the fact that heating or cooking with a microwave oven is generally more critical with respect to time than is conventional heating or cooking. It is not practical to attempt to simultaneously heat or cook several food products having different temperature requirements or energy absorbing characteristics. Furthermore, it is not practical to prepare one set of cooking instructions, based on time, which would be universally applicable to all microwave ovens.
Cooking experiments, especially with meats and the like, have shown that the internal temperature of the food product is the most reliable means to determine the degree of doneness. By the same token, external temperature of the food product does not correlate well with its degree of doneness. Some microwave ovens are equipped with a probe to detect the internal temperature of a food product being cooked therein and to turn off the oven when a predetermined internal temperature level is achieved. Nevertheless, in most cases only one food product can be cooked in the microwave oven at any given time.
The present invention is directed to a vessel for foods to be prepared in a microwave oven, the vessel being reflective to microwave energy and being provided with one or more apertures allowing passage of the microwave energy to the food product within the vessel. Shielding means are provided to close the one or more apertures so that the food product within the vessel is no longer subjected to substantial microwave energy. The shielding means is shifted from an aperture open position to an aperture closed position in response to a predetermined internal temperature of the food product within the vessel. Depending upon the precision with which the vessel and shielding means are made, the shielding means in its aperture closed position can reduce the microwave energy transmitted to the food product to virtually zero.
Since the vessel of the present invention is responsive to a predetermined internal temperature of the food product contained therein, the operator of a microwave oven is enabled to cook several food products with differing temperature requirements at the same time, when each food product is contained in a vessel of the present invention. With the use of such a vessel, food products can be heated or cooked in accordance with a single set of cooking instructions based on the internal temperature of the food product, regardless of the power output of the particular microwave oven being used. The vessel of the present invention may be made so as to be disposable or so as to be reusable.